Early Stage Researchers – 1st Authorship

The Black Hole Mass Function across Cosmic Time. II. Heavy Seeds and (Super)Massive Black Holes

Alex Sicilia (SISSA), Andrea Lapi, Lumen Boco, Francesco Shankar, David M Alexander, Viola Allevato, Carolin Villforth, Marcella Massardi, Mario Spera, Alessandro Bressan, Luigi Danese

The Astrophysical Journal, Volume 934, Issue 1, July 2022, https://doi.org/10.3847/1538-4357/ac7873

ABSTRACT: This is the second paper in a series aimed at modeling the black hole (BH) mass function from the stellar to the (super)massive regime. In the present work, we focus on (super)massive BHs and provide an ab initio computation of their mass function across cosmic time. We consider two main mechanisms to grow the central BH that are expected to cooperate in the high-redshift star-forming progenitors of local massive galaxies. The first is the gaseous dynamical friction process, which can cause the migration toward the nuclear regions of stellar mass BHs originated during the intense bursts of star formation in the gas-rich host progenitor galaxy and the buildup of a central heavy BH seed, M ∼ 103−5 M, within short timescales of ≲some 107 yr. The second mechanism is the standard Eddington-type gas disk accretion onto the heavy BH seed through which the central BH can become (super)massive, M ∼ 106−10 M, within the typical star formation duration, ≲1 Gyr, of the host. We validate our semiempirical approach by reproducing the observed redshift-dependent bolometric AGN luminosity functions and Eddington ratio distributions and the relationship between the star formation and the bolometric luminosity of the accreting central BH. We then derive the relic (super)massive BH mass function at different redshifts via a generalized continuity equation approach and compare it with present observational estimates. Finally, we reconstruct the overall BH mass function from the stellar to the (super)massive regime over more than 10 orders of magnitudes in BH mass.


Simulations of 60FE entrained in ejecta from a near-Earth supernova: effects of observer motion

Evgenii Chaikin (ULEI), Alexander A Kaurov, Brian D Fields and Camila A Correa

Monthly Notices of the Royal Astronomical Society, Volume 512, Issue 1, May 2022, Pages 712–727, https://doi.org/10.1093/mnras/stac327

ABSTRACT: Recent studies have shown that live (not decayed) radioactive 60Fe is present in deep-ocean samples, Antarctic snow, lunar regolith, and cosmic rays. 60Fe represents supernova (SN) ejecta deposited in the Solar system around 3Myr3Myr ago, and recently an earlier pulse ≈7 Myr≈7 Myr ago has been found. These data point to one or multiple near-Earth SN explosions that presumably participated in the formation of the Local Bubble. We explore this theory using 3D high-resolution smooth-particle hydrodynamical simulations of isolated SNe with ejecta tracers in a uniform interstellar medium (ISM). The simulation allows us to trace the SN ejecta in gas form and those eject in dust grains that are entrained with the gas. We consider two cases of diffused ejecta: when the ejecta are well-mixed in the shock and when they are not. In the latter case, we find that these ejecta remain far behind the forward shock, limiting the distance to which entrained ejecta can be delivered to ≈100 pc in an ISM with nH=0.1cm−3nH=0.1cm−3 mean hydrogen density. We show that the intensity and the duration of 60Fe accretion depend on the ISM density and the trajectory of the Solar system. Furthermore, we show the possibility of reproducing the two observed peaks in 60Fe concentration with this model by assuming two linear trajectories for the Solar system with 30-km s−1 velocity. The fact that we can reproduce the two observed peaks further supports the theory that the 60Fe signal was originated from near-Earth SNe.


The Black Hole Mass Function Across Cosmic Times I. Stellar Black Holes and Light Seed Distribution

Alex Sicilia (SISSA), Andrea Lapi (SISSA), Lumen Boco, Mario Spera, Ugo N Di Carlo, Michela Mapelli, Francesco Shankar (SOTON), David M Alexander (UDUR). Alessandro Bressan, Luigi Danese

arXiv:2110.1607v1 (astro-ph.GA), 29 October 2021, https://arxiv.org/abs/2110.15607#

ABSTRACT: This is the first paper in a series aimed at modelling the black hole (BH) mass function, from the stellar to the intermediate to the (super)massive regime. In the present work we focus on stellar BHs and provide an ab-initio computation of their mass function across cosmic times. Specifically, we exploit the state-of-the-art stellar and binary evolutionary code \texttt{SEVN}, and couple its outputs with redshift-dependent galaxy statistics and empirical scaling relations involving galaxy metallicity, star-formation rate and stellar mass. The resulting relic mass function dN/dVd log m. as a function of the BH mass m. features a rather flat shape up to m∙≈50M⊙ and then a log-normal decline for larger masses, while its overall normalization at a given mass increases with decreasing redshift. We highlight the contribution to the local mass function from isolated stars evolving into BHs and from binary stellar systems ending up in single or binary BHs. We also include the distortion on the mass function induced by binary BH mergers, finding that it has a minor effect at the high-mass end. We estimate a local stellar BH relic mass density of ρ∙≈5×107M⊙ Mpc−3, which exceeds by more than two orders of magnitude that in supermassive BHs; this translates into an energy density parameter Ω∙≈4×10−4, implying that the total mass in stellar BHs amounts to ≲1% of the local baryonic matter. We show how our mass function for merging BH binaries compares with the recent estimates from gravitational wave observations by LIGO/Virgo, and discuss the possible implications for dynamical formation of BH binaries in dense environments like star clusters. [abridged]